A gypsum board is frequently used as a material for building since it has a fire resistance, a sound insulating property, etc., and is economic. Such a gypsum board is a plate-type structure obtained by covering a core material based on gypsum (referred to as “core” below) with a base paper for gypsum board (referred to as a “base paper” below), and a gypsum board product with a thickness of 12.5 mm is composed of approximately 93% by weight (abbreviated as “%” below) of gypsum and approximately 7% of a base paper. The gypsum board is used throughout a building and the remaining end part(s), etc., (as referred to as a “waste material”, and a waste material produced in a new building site is referred to as a “new building waste material” and a waste material produced in a demolition site is referred to as a “demolition waste material”, below) cut out depending on the dimensions of a used part is/are produced in a building site. The production rate of new building waste materials is deduced to be approximately 10% of the used amount at the time of building and, as the annual usage of gypsum boards being approximately five million tons is taken into consideration, approximately 50 million tons of new building waste materials are consequently produced as industrial wastes. Also, the production quantity of demolition waste materials produced by the demolition of an existing building was approximately 90 million tons in the year 2002, according to estimation by an aggregate corporation, Gypsum Board Industry Association, and it is expected that the production quantity of demolition waste materials will increase in future.
In regard to new building waste materials among these waste materials, recycle routes such as a wide-area recycling industry route approved by the environment ministry and intermediate processing industry routes approved by prefectural governor are established and approximately 50% of the production quantity of new building waste materials is utilized as a material for manufacturing a new gypsum board. On the other hand, the remaining new building waste materials and demolition waste materials are dumped in landfill, etc., similarly to other industrial wastes. However, a waste gypsum board to which a paper has adhered is dealt as an industrial waste of controlled type and further promotion of separation recycle is socially desired with the lack of the capacity of remaining landfill space and the implementation of Construction Material Recycling Act.
As described above, although the increase of the recycle rate for a waste material in future is expected, the recycle of a gypsum board waste material to a raw material of gypsum at present is conducted by, first, coarsely breaking a waste material of gypsum board into a size of approximately 10 cm square, then finely breaking the coarsely broken waste material of gypsum board into a size of approximately several cm square, screening the broken waste material according to need to separate paper pieces of a base paper for gypsum board from the broken waste material and subsequently compounding gypsum of the broken waste material of gypsum board into gypsum of a common raw material for gypsum board. However, when the gypsum component remains dihydrate gypsum, if the broken waste material is subjected to screening, the weight of gypsum component having adhered to separated paper pieces is 50% or greater of the weight of the paper pieces, and even though the screened waste material is further subjected to screening, the gypsum component having adhered to the paper pieces is reduced by only 5-10%. It is considered that the cause of the adhesion of the gypsum component to the paper pieces is that the gypsum component of dihydrate gypsum is a needle crystal and is deeply embedded into the paper pieces of the base paper for gypsum board. In addition, when a waste material of gypsum board is moisturized or wetted, the problem is that trouble such as the adhesion of the waste material to a transportation apparatus for transporting the waste material, clogging of a screening apparatus, etc., is easily caused.
Also, when recycle rate of waste material is low, for example, approximately 5%, a serious problem is not made even though the entire quantity of a paper component is directly recycled. However, the recycle rate of the waste material is approximately 10% or greater, the recycle of the entire quantity of the paper component is not preferable since the fire resistance property of a gypsum board product may be lowered due to the increase of the content of the paper component in the core of the product and more kneading water is required in the manufacture of a gypsum board. Also, the problem occurs that paper pieces are dispersively found in the core portion of the product and the appearance of a gypsum board product degrades accordingly. Thus, the recycle of the entire quantity of the paper component is limited with respect to fireproof, productivity, quality, etc. Therefore, in order to improve the recycle rate of a waste material, the elimination of a paper component from the waste material is becoming inevitable.
On the other hand, in regard to paper pieces separated from a waste material of gypsum board, the less a gypsum component having adhered to the paper pieces is, the more paper pieces can be recycled for a raw material for waste paper, a raw material for agriculture (for fertilizer) and other industrial applications. Therefore, a method for separating paper pieces containing a little gypsum component from the waste material of gypsum board is much needed.
The following Japanese Laid-Open Patent Application No. 06-142638 and Japanese Laid-Open Patent Application No. 08-176985 can be listed as documents for conventional techniques which have relevance with the invention of the subject application.
Japanese Laid-Open Patent Application No. 06-142638 discloses a method for recovering a base paper for gypsum board and gypsum from a waste material of gypsum board, characterized in that after a waste material of gypsum board is heated in which a base paper for gypsum board has adhered to at least one part of a gypsum core, water is supplied to the waste material of gypsum board to separate the base paper for gypsum board from the gypsum core and gypsums constituting the separated base paper for gypsum board and gypsum core are recovered, respectively.
Herein, as a method for recovering the base paper, there are disclosed a method of dipping the waste material of gypsum board in a water tank after heating (and cooling) it and recovering paper floating on water surface (floatation separation method), a method of supplying water to a heated gypsum board, etc. Also, this document discloses, as a practical example, the entire quantity (1.31 kg) of paper pieces to which burnt gypsum had adhered was thrown into 20 liters of water and after shortly agitating operations of recovering the paper pieces on a screen were repeated three times whereby the burnt gypsum had adhered to the paper pieces could be completely washed out and paper pieces to which no gypsum adhered (dry weight: 693 g) were obtained.
However, specific means and conditions for continuously water-wash treating paper pieces to which gypsum has adhered is not disclosed or suggested.
Also, Japanese Laid-Open Patent Application No. 08-176985 discloses a paper material washing apparatus provided with a device for supplying washing water to a paper material in a rotatably lying air and water through-flow drum having both a paper material inlet at one side of the air and water through-flow drum and a paper material outlet at the other side thereof, which apparatus is a rotary drum-shaped washing apparatus capable of drastically improving the dispersion effect of a fiber component and replacement and washing effect (deinking and dust removing effect), wherein baffle plates extending along the internal peripheral surface of the air and water through-flow drum in the peripheral direction are arranged with intervals in the axial direction and scrape up plates for scraping up paper material liquid to the drum revolving direction are arranged with intervals between the adjacent baffle plates in the peripheral direction, and wherein a paper material thrown into the paper material inlet overflows each of washing zones formed between the baffle plates one by one and reaches the paper material outlet and the scraping up to the peripheral direction of the paper material by the scrape up plates and the flowing downward of it by gravity are repeated by the revolution of the air and water through-flow drum in each of the washing zones between the baffle plates.
However, there is not disclosed or suggested that, after pretreatment such as preparatory breaking and paper piece separation is applied to a waste material of gypsum board, a rotary drum-shaped washing apparatus is used for washing separated paper pieces.